The present invention relates to a mass spectrometer and a method of mass spectrometry.
It is well known to those skilled in the art of mass spectrometer design that the analysis of complex mixtures, such as those found in proteomics, is especially challenging. Multiple approaches have been employed including Data Directed Analysis (“DDA”) where ions of interest are determined using a survey scan. Parent or precursor ions of interest are then sequentially isolated and fragmented or reacted to generate product ion spectra. Both the product ion spectra and precursor ions are then used to identify components. However, such techniques suffer from the problem of low duty cycle since whilst the parent or precursor ions are individually isolated and analysed other parent or precursor ions are lost. Furthermore, these techniques tend to be biased towards ions of particular intensities.
An improvement over the DDA methodology is to use an approach known as Shotgun or MSE wherein an ion beam is rapidly switched between a non-product ion forming mode (i.e. low collision energy) and a product on forming mode (i.e. high collision energy). According to the known approach, product ions are assigned to precursor ions based upon one or more characteristics of their chromatographic elution profile. This known approach benefits from high duty cycle and unbiased data acquisition but can suffer from a lack of specificity as multiple precursor ions can co-elute.
The known Shotgun or MSE approach may be categorised as being a high duty cycle approach having reduced specificity in contrast to the known DDA approach which may be categorised as having high specificity but a low duty cycle.
It is desired to provide a method that has the benefit of high duty cycle and unbiased data acquisition but which also has an improved specificity compared with the known Shotgun or MSE approach.